The dopamine transporter (DAT) and mu opiate receptor (MOR) have been identified as the principal brain receptor sites correlated with the rewarding and euphoric properties of cocaine and morphine. Cellular and subcellular localization data are important to help to elucidate the functional properties of these important brain molecules. In this FY, studies of the distribution of the DAT and MOR proteins in rat brains were reported. Ultrastructural studies of the transporter revealed that most of the DAT and MOR immunoreactivity was found in intracellular and plasma membrane localizations not readily associated with conventional synaptic specializations. These studies substantially add to information on the detailed cellular localizations of these important sites for cocaine and morphine reward. They underscore the likelihood that extrasynaptic removal of dopamine provides a principal function of DAT.